1. Field of the Invention
The present invention generally relates to a tool and a method for repairing the threads within a bore. More particularly, the invention relates to a tool and a method for repairing the threads within a bore of the head of an internal combustion engine without the danger of metallic particulates and combustion by-products falling into the engine housing.
2. Description of the Prior Art
According to the teachings of the prior art, one problem which is being encountered with servicing automobiles can be attributed to the manufacture of contemporaneous internal combustion engines from soft materials such as aluminum and the like. Spark plugs used by these engines tend to destroy spark plug openings when the hard metal thread of a spark plug has burrs on it or is cross threaded and by the repeated insertion and removal of a spark plug especially if tightened too securely.
The problem can be remedied in several ways such as removing the engine head, boring out the spark plug openings, rethreading the openings, and replacing the spark plug with a larger diameter spark plug or with an insert to reduce the threaded openings to the proper size. However, such procedure can be financially burdensome to the automobile owner.
Alternatively, a procedure in which the engine head is not removed, encounters the possibility that metallic particulates could remain within the cylinder to become caught between valves and their seats causing burned valves. Furthermore, metallic particulates in the cylinders of an internal combustion engine could readily cause numerous other problems if such particulates become wedged between the pistons and cylinders during the reciprocation process.
Representative of the prior patent art directed at this problem are U.S. Pat. Nos. 1,196,415 (Abrahmson); 2,212,753 (Smila et al.); 2,948,000 (Borland); 3,694,838 (Runton); 3,750,259 (Timmons); 3,847,499 (Heyworth et al.); 3,864,806 (Hanson et al.); and 4,539,832 (Koller).
Of general interest are U.S. Pat. No. 1,196,415 which discloses an implement for truing-up threads particularly the valve and cap threads of nipples of pneumatic tires; U.S. Pat. No. 2,212,753 which discloses a reaming tool for boring holes of relatively great depth; U.S. Pat. 3,864,806 which discloses a method for repairing stripped spark plug threads in engine heads; and U.S. Pat. No. 4,539,832 which discloses a hole sizing tool to push malleable material from the walls of an oversized hole toward the axis of the hole to reduce the effective diameter of the hole.
Of particular interest are U.S. Pat. Nos. 2,948,000; 3,694,838; 3,750,259; and 3,847,499. U.S. Pat. No. 2,948,000 discloses a combination tapped hole and seat refinishing tool comprising an enlarged head mounted at the upper end of a shank with a wider lower portion, means integral with the lower portion of the shank for cleaning a tapped hole, and means slidably mounted on the shank for scraping the seat around the hole. The lower tip of the shank forms an unthreaded pilot and the scraping means includes a collar slidably mounted on the shank. The collar has a vertical keyway, a pin mounted transversely through the shank and extending into the keyway. The collar also has cutting teeth on its bottom edge, a coil spring surrounding the upper end of the shank, and a lower stop means.
U.S. Pat. No. 3,694,838 discloses a rotary tool for reworking spark plug ports of soft metal cylinder heads comprising a handle part and a working part. The handle part has an internally threaded bore adapted to engage the entering end of the working part after the working part has penetrated through the cylinder head. The working part has a first and second reamer section of smaller and larger diameter followed by a tapered lead-in section, a tapping section, and a third reamer section for producing a countersink at the mouth of the spark plug port to receive the head flange of a hard metal insert.
U.S. Pat. No. 3,750,259 discloses an assemblage of components for repairing the threads of a through bore comprising a reamer tool with a pilot end portion for forming an oversize bore and with a tail portion for forming a counterbore at the outer end of the over-size bore. Further comprising a right hand threaded tap for forming right hand threads in the over-size bore, a right hand threaded shank engageable in an inside and outside right hand threaded sleeve-type insert, and a threaded nut-type flaring tool for flaring the first inserted end of the sleeve insert in the corresponding end of the threaded over-size bore.
U.S. Pat. No. 3,847,499 discloses a tool for preparing a damaged opening in a rotary engine housing to receive a threaded insert comprising an alignment block, a securing bolt, a guide pin, and reamer and tap assemblies. The alignment block has a first and second opening for alignment with undamaged and damaged spark plug openings in communication with a common combustion chamber. The securing bolt clamps the alignment block to the housing and has air conduit means for communication of the combustion chamber. The reamer and tap assemblies are receivable by the alignment block opening.